1. Field of the Invention
The present invention relates to a method for the manufacture of a molded member from a ceramic material, for instance of silicon nitride or silicon carbide, wherein the molded member, which is arranged in an evacuated capsule of a high temperature-resistant glass, is compressed into a non-porous condition under a pressure acting on all sides thereof. The starting material of the glass capsule is applied onto the molded members in a non-vitrified state and exposed under a vacuum to its reaction temperature until there is formed a molded member-encompassing, cohesive glass layer which constitutes the capsule. This method is generally and summarily designated as high-temperature isostatic pressing. The object of the method is to compress a ceramic member having a porosity of up to about 30% under a pressure uniformly acting thereon on all of its sides up to non-porosity in order to increase its strength.
2. Discussion of the Prior Art
A prerequisite for being able to increase the density of the ceramic member lies in the evacuation of its pores. The molded members are produced in the form of pressings or briquettes, which are surrounded by a capsule or envelope. At present, known are the following approaches to the manufacturing of such pressings:
1. Encapsulation of ceramic powder in glass molds.
2. Encasing of reaction-sintered molded members by dipping them into liquefied glass.